The objectives of the research proposed in this application are to develop an in vitro method of cultivating virulent Treponema pallidum in cell-free medium and to develop a method of immunization for syphilis. Studies will be conducted to determine the growth requirements and immunogenicity of Treponema hyodysenteriae, a new cultivatable pathogenic species of Treponema. The information concerning the growth requirements of this organism will be applied to the development of a cultivation medium for T. pallidum. Attempts will be made to grow both Nichol's rabbit-adapted strain and human syphilitic chancre strains of T. pallidum. If T. pallidum can be propagated in vitro, its nutritional requirements and immunogenic properties will be determined.